Sensitization and radiation hardening of the photostimulable X-ray storage phosphor CsBr:Eu2+

The X-ray storage phosphor CsBr:Eu²⁺ in form of needle image plates is believed to be a promising alternative to the granular BaFBr:Eu²⁺ with regard to PSL yield and spatial resolution. Unfortunately, CsBr:Eu²⁺ exhibits poor radiation hardness, which is caused by a migration of europium ions initiated by naturally existing defect centers like (Eu²⁺-V_Cs)-centers and X-ray generated M_Eu-centers. It will be shown that the formation of (Eu²⁺-O^2?)-dipoles at the expense of (Eu²⁺-V_Cs)-dipoles, incorporated by thermal annealing in O₂-containing and humid atmosphere, does not improve the radiation stability. There is, however, a strong improvement in the radiation hardness by codoping of CsBr:Eu²⁺ with lithium ions, which is accompanied by a complete suppression of the previously observed M_Eu-center formation.